HID Grow Light Distance for Growing Cannabis

Light Distances for Growing Cannabis with HID Lighting
HID grow lights like Metal Halide and HPS (High Pressure Sodium) are the most widely-used and debatably the highest-yielding grow lights available for growing cannabis.

Metal Halide lights are well-suited to the vegetative stage and tend to encourage plants to grow short and squat though they are less electrically efficient than HPS. HPS grow lights are suitable for both the vegetative and flowering stage of cannabis growth and the light they give off encourages plants to quickly grow tall and produce big buds. Despite these differences, MH and HPS bulbs need to be kept about the same distance away from your plants. The proper distance actually depends on the size/wattage of your lamp.

In addition to the wattage, it’s important to realize that older bulbs stop giving off as much light over time, so new MH/HPS bulbs generally need to be kept further away and older bulbs should be kept closer than the normal recommendations.

If you’re using new bulbs, never start closer than the “~Sunlight” distance on the chart and only move lights closer if your plants are stretching towards the light (getting tall and lanky).

If you’re using older MH/HPS bulbs, you should replace them if you can, but if that’s not possible you can keep your bulbs closer to help make sure your plants are still getting good light levels. This is why it’s beneficial to be able to test your current light levels with a lux meter.

In general, MH bulbs need to be replaced about once a year (every 2-3 grows), while HPS grow lights last a bit longer, up to 2 years (every 4-5 grows). Older HID bulbs give off less light and more heat, so in addition to keeping the right distance, make sure you’re aware of the age of your bulbs. To maximize the light to my plants in the flowering stage, I personally replace HPS bulbs every 3rd grow, but that’s a bit excessive.

If you see that all the leaves are turned up toward the light, it’s a sign your plants may be getting too much light. This puts them at risk of getting light burn unless the light gets moved up.

HID stands for High Intensity Discharge. These are the most common kind of indoor grow light. These bulbs come in 3 main varieties:
Along with the different spectrums, these lights will come at different levels of wattage. Ranging from 250, to 1000 watts. The higher the wattage, the more heat will be produced. So the lights distance from the top of the plants will differ according to the wattage of the bulb you are running.
On average, most HID grow lights will be around 14-18 inches from the top of the canopy. This is a good level, where heat isn’t too high, but the plant receives a large amount of light.

Temperatures can become an issue when growing with HID lighting, and in some cases, growers will use a “cooling tube” or “cooling hood” to help control excessive heat.

This will have an affect on the amount of light your plant will receive, so if you’re using a cooling tube, try and get the light a little closer to the plants.

HID Grow light distance from seeds?
You should be using mh bulb for veg. Hps is for flowering.
If you have the light too far your plants will stretch. I'd say you could go to at least 16 inches. A lot depends on your temps in your grow room or grow tent to. 

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